1. Field of the Invention
The present invention relates to improvements in an image-forming apparatus wherein a photosensitive medium is image-wise exposed to a radiation.
2. Discussion of the Prior Art
There is known an image-transfer or image-forming apparatus which has an exposing device for forming latent images on a photosensitive medium, and a developing device for developing the latent images into visible images. Usually, an electrostatically chargeable photosensitive paper or a pressure-sensitive photosensitive paper is used as the photosensitive medium. The electrostatically chargeable photosensitive paper includes an electroconductive base, and a photoconductive layer formed on one surface of the electroconductive base. The photoconductive layer contains an photoconductive material, for example, an inorganic pigment such as ZnO and TiO.sub.2, which is dispersed in a binder resin. The pressure-sensitive photosensitive paper has a multiplicity of microcapsules whose hardness is changed upon exposure to a radiation. In a developing process, the microcapsules which have been softened or remain uncured after the exposing process are ruptured due to a pressure applied to the paper, so that a chromogenic material comes out of the ruptured microcapsules and reacts with a developer material, to form visible images corresponding to latent images that are formed on the paper in a prior exposing process wherein the microcapsules are image-wise exposed to a radiation.
In the case where the electrostatically chargeable photosensitive paper is used, its electrostatically chargeable surface must be protected against scratching, rubbing or friction, to insure a high quality of the visible images to be formed. The pressure-sensitive photosensitive paper is also sensitive to scratching, rubbing and friction, which may cause a reaction of the chromogenic material with the developer material. Where the photosensitive medium is supplied in the form of cut sheets superposed on each other in stack, a sheet feeding device for feeding the cut sheets one after another must be provided with suitable protective means for preventing the cut sheets from being scratched or rubbed or otherwise subjected to undesirable image-forming actions during a sheet feeding operation. Such protective means for avoiding deterioration of the visible images finally obtained on the cut sheets will inevitably lead to increased structural complexity and size of the sheet feeding device.
In the case where the photosensitive medium is provided in the form of a web wound as a roll, the web is fed with a reduced possibility of scratching, rubbing or other image-forming actions. Further, since the feeding device is not required to handle individual cut sheets, the feeding device can be comparatively simple in construction and small-sized.
In a known image-forming device using a feeding device adapted to feed a photosensitive medium in the form of a web from a supply roll, the photosensitive web is cut at a position downstream of the developing device, that is, after the exposed portion is developed. This arrangement suffers from a relatively low utilization ratio or yield of the photosensitive medium. Described more specifically, a developing toner has been deposited on the surface of an unexposed portion of the photosensitive web which has passed the developing device, more precisely, an unexposed portion between the developing device and a shearing device. If the pressure-sensitive photosensitive web is used, a reaction between the chromogenic material from the ruptured microcapsules and the developer material has been initiated on the unexposed portion of the web which has passed the developing device. Therefore, the unexposed portion which has been subjected to a developing process cannot be reused, and must be removed.